In the manufacture of continuous glass filaments, glass is melted in a filament forming apparatus and flows to one or more bushings. Each bushing has a number of nozzles or tips through which streams of molten glass flow. The glass streams are mechanically pulled from the nozzles by a winding apparatus to form continuous glass filaments.
The temperature of the molten glass within the bushing must be high enough to maintain the glass in a liquid state. However, if the temperature is too high, the molten glass will not cool sufficiently so as to become viscous enough to form filaments after passing through the bushing tips. Thus, the glass must be quickly cooled or quenched after it flows from the bushing tips and forms glass filaments. If the glass cools too slowly, the glass filaments will break and the filament forming process will stop.
There are numerous apparatuses for cooling the glass filament forming area beneath a filament forming machine. Conventional cooling apparatuses use air, water, or both to transfer heat from the filament forming area beneath a bushing and cool the glass filaments.
An example of a glass filament forming apparatus is disclosed in U.S. Pat. No. 3,708,271 to Loewenstein et al., the disclosure of which is expressly incorporated herein by reference. A conventional glass filament forming apparatus 5 with a cooling apparatus 50 is shown in FIGS. 1 and 2. Filaments 20 are drawn from a plurality of nozzles 12 of a bushing 10 and gathered into a strand 22 by a roller 42. Size is applied to coat the filaments by a size applicator 40. A reciprocating device 34 guides strand 22, which is wound around a rotating collet 32 in a winding apparatus 30 to build a cylindrical package 24.
Cooling apparatus 50 is located beneath the bushing 10 to cool the filament forming area 14. As shown in FIG. 2, cooling apparatus 50 includes a manifold 52. Manifold 52 preferably includes one or more internal channels that extend along the longitudinal axis of the manifold 52.
Cooling apparatus 50 includes a plurality of cooling fins 70. Each cooling fin 70 is a solid, thin strip of metal, such as copper. Cooling fins 70 may be cantilevered from a single water-cooled manifold or may be secured at each end to a pair of water-cooled manifolds. Each cooling fin 70 extends between adjacent rows of nozzles 12. Filaments 20 drawn from the bushing 10 pass on either side of a cooling fin 72.
Heat from the glass is radiantly and convectively transferred to the fins 70 as the glass flows from the nozzles 12 and is drawn into free continuous filaments 20. The heat passes conductively through the fins 70 and to the water-cooled manifold 52. Cooling fins 70 increase the surface area of the cooling apparatus 50, thereby increasing the amount of heat that can be transferred from the filament forming area.
A cooling fluid supply 54, such as water, enters the manifold 52, travels through a channel, and exits the opposite end of the manifold as a cooling fluid return 56. The cooling fluid absorbs heat as it flows through the manifold 52, thereby cooling the manifold 52, cooling fins 70, and indirectly, the filament forming area 14.
The amount of heat that this cooling apparatus can remove from the filament forming area 14 is limited. Heat must travel through the cooling fins 70 and manifold 52 before it is absorbed by the cooling fluid flowing through the manifold.
Another conventional cooling apparatus having a manifold 52 and cooling fins 70 is shown in FIG. 3. Examples of this type of known cooling apparatus are disclosed in U.S. Pat. No. 3,746,525 to Kasuga et al., U.S. Pat. No. 4,824,457 to Jensen, and U.S. Pat. No. 5,244,483 to Brosch et al.
Manifold 52 includes two cooling fluid channels 58, 60. Initially, cooling fluid flows into channel 58 via cooling fluid supply 54. The cooling fluid flows from the manifold 52 into and around the U-shaped passage 72 in the cooling fin 70 and exits the fin 70 into channel 60. The cooling fluid exits the manifold 52 through fluid return 56. As apparent to the artisan, this cooling apparatus 50 removes more heat from the filament forming area than the apparatus in FIGS. 1 and 2 because water flows inside of the cooling fins 70. However, the amount of heat that can be absorbed by the cooling fluid in cooling apparatus 50 is still limited.
If heat can be more rapidly removed from the filament forming area beneath a bushing, the operating temperatures of the bushing and the molten glass in the bushing can be increased, thereby allowing overall throughput to be increased. Accordingly, there is a need for improved apparatus for and method of cooling a filament forming area beneath a bushing to remove a greater amount of heat.